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Some New Zealand Parasitic Copepoda of the Family Anthosomidae

Aethon, Krøyer, 1836

Aethon, Krøyer, 1836

Anthosomidae. Male probably unknown. Female: Head fused with first thoracic segment, cephalothorax usually with lateral wing-like expansions; second and third thoracic segments fused but with separate dorsal plates, and with lateral expansions which extend slightly posterolaterally but do not fuse with plate of fourth segment; fourth segment covered by a dorsal plate which extends posteriorly to hide the posterior part of the body and all or most of the egg strings in dorsal view; genital segment small, abdomen small and rounded; caudal laminae small, irregular in outline with a lateral spine-bearing projection and further spines posteriorly; eggs uniserriate, flattened; egg strings long, coiled between third pereiopods and plate of fourth thoracic segment; first antenna with six or seven segments, several with short setae; second antenna subchelate; mandibular palp with two rami, at least one with spines; maxilla of two segments usually with rows of spines distally; maxilliped subchelate; first four pereiopods biramous; first pereiopods with rudimentary one-segmented rami; second pereiopods held at right angles to body, rami fused with basipod; third pereiopods large, thickened lamellae with endopod covering egg strings in ventral view and exopod hiding them in lateral view; fourth pereiopods lamellar, divided nearly to base, about half length of third pereiopods, which completely hide them in ventral view; fifth pereiopods uniramous, rudimentary.

Parasites on marine teleosts.

Type species: Aethon quadratus Krøyer, 1836.

Aethon percis (Thomson, 1889)

Lernanthropus percis Thomson, 1889, p.336-7, pl. 27, figs. 2a-j
nec              "              "              "             Wilson, 1936, p.340.

Material

From gills of Parapercis colias (blue cod):

One female, collected at the northern end of Kapiti Is., by the author, 4 February 1967; three females from the collection of the Otago Museum in a tube containing three labels "Lernanthropus percis—gills of blue cod", "G.M.T. dep. 1910" and "label on outside of tube—from gills of blue cod 23/10/79" (there is now no label page 13on outside of tube). One of these latter specimens had been dissected and may be the specimen from which Thomson made his original description and drawings.

Description

Female (figs. 37-50).

Overall length (5.15 mm - 5.73 mm).

Cephalothorax, width four-fifths length (1.63 mm - 1.95 mm × 1.18 mm - 1.47 mm), subovate, posterior margin sublinear, raised in a ridge; antennae borne laterally on a short anterior area, one-third carapace width posteriorly, narrowing to two-thirds this width anteriorly, anterior margin straight, marked off from carapace by lateral grooves, extending a little beyond anterior margin of remainder of cephalothorax; lateral margin of carapace expanded as two lobes, each half length of margin, anterior lobe bulging posterolaterally, posterior lobe bulging anterolaterally, posterior lobe slightly bifid distally in some specimens, posterior lobe sometimes unequally developed (see fig. 37 in which right hand lobe is larger than left).

Second and third thoracic segments fused, but distinguished by a groove which runs dorsally and laterally; combined length three-quarters width, second segment four-fifths width of third (combined length 1.05 mm - 1.21 mm, second segment width 1.13 mm - 1.39 mm, third segment width 1.44 mm - 1.67 mm), second and third segments each with most of dorsal surface covered by a poorly developed plate; lateral margin of combined second and third thoracic segments extend laterally as wing-like expansions, which increase the width by up to one-fifth, lateral margins of expansions sublinear, anterior angles rounded, posterior angles extended posterolaterally for a distance equal to two-fifths combined segments length, narrowing and rounded distally, not fused with plate of fourth segment.

Fourth thoracic segment including plates, slightly longer than wide (2.43 mm - 3.32 mm × 2.47 mm - 2.87 mm), lateral margins sublinear and parallel for the anterior four-fifths of their length, then slightly angled, posterior margin an entire curve except for a concave invagination medially which is one-sixth plate width, and one-eighth length of plate; actual segment short, length one-third width (0.72 mm - 0.80 mm × 2.11 mm - 2.53 mm), subrectangular, angles rounded.

Genital segment subrectangular, a little wider than long (0.42 mm × 0.49 mm), widest anteriorly, narrowing to two-thirds this width distally.

Abdomen subovate, as wide as long (0.55 mm × 0.53 mm), fused to genital segment anteriorly, bearing caudal laminae posterolaterally.

Caudal laminae very small, length twice width (0.18 mm × 0.09 mm), subtriangular, lateral margins irregular, with a lateral projection one-quarter distance from base, one-fifth as long as a lamina, a little wider than long, and tipped with a sharp spine; lamina with a further sharp spine at the distal apex, and further spine on medial margin near the apex.

Egg strings long, complexly coiled and hidden in dorsal view by the plate of the fourth thoracic segment, in ventral view by the third pereiopods.

First antenna of seven subrectangular segments, ratio of length from the basal segment outwards being approximately 3:3:2:3:1:1:1; first segment width two-thirds length, with a small spine on outer margin, second segment width four-sevenths length, with three setae on outer margin, third segment as wide as long, with a small seta on outer margin, fourth segment width half length, with one long and one short seta on outer margin (fig. 40 shows fourth segment joined to fifth by a short membrane which could be a thinly chitinised segment), fifth segment as wide page 14

Aethon percis (Thomson, 1889) female: fig. 37: dorsal view; fig. 38: lateral view; fig. 39: ventral view; fig. 40: first antenna; fig. 41: second antenna; fig. 42: mandibular palp; fig. 43: maxilla; fig. 44: tip of maxilla; fig. 45: maxilliped; fig. 46: first pereiopod; fig. 47: second pereiopod; fig. 48: fourth pereiopod; fig. 49: genital segment, abdomen and caudal laminae; fig. 50: caudal lamina.

page 15 as long, with two small setae on outer margin, sixth segment as wide as long, with one small seta on outer distal angle seventh segment rounded distally, width three-quarters length, with six setae on distal margin.

Second antenna of two segments, subchelate; first segment, basal width half length, narrowing to three-quarters this width distally, curved, with a stout spine on inner margin near base; second segment basal width half length, narrowing steadily to a sharp point distally, strongly curved, with a stout spine near inner margin one-quarter of distance from base.

Month tube small (0.5 mm in length), sharply pointed distally.

Mandibular palp, with two rami on a flattened subrectangular base; outer ramus, width two-fifths length, rounded distally, with two setae and one subrectangular process distally; inner ramus half length of outer, width two-thirds length, rounded distally, with two setae distally.

Maxilla of two segments, segments subequal in length; first segment, basal width half length, narrowing slightly distally, distal margin rounded; second segment basal width one-tenth length, narrowing gradually distally except that distal seventh narrows suddenly and bears a longitudinal row of small spines reaching almost to the slightly blunted tip, a small process, one-third length of narrowed distal region, width half length, is situated near inner margin one-quarter distance from tip, and bears two setae distally, the larger setea subequal in length to process, the other a little smaller.

Maxilliped of two segments, subchelate; first segment, basal width two-thirds length, narrowing slightly distally, distal margin rounded; second segments basal width half length, narrowing gradually to a distal point, sharply curved over distal two-thirds, with a small spine on inner margin one-third distance from base.

First pereiopod biramous, each ramus of one segment; basipod swollen, subsemicircular, length two-thirds width, with one small spine medial to endoped and another on a raised boss lateral to exopod; exopod subovate, subequal in length to basipod, width half length, with five flattened spines on distal margin; endopod subtriangular, subequal in length to exopod, basal width half length, distal apex bearing a spine.

Second pereiopod biramous, the rami fused to the basipod, length including rami more than twice length of first pereiopod, as long as basal width, narrowing steadily distally, to end in a sharp point, the terminal section presumed to include the endopod, distal portion curving sharply medially and posteriorly away from the body, inner margin with a well developed subtriangular expansion one-third distance from base, and a further process on outer margin two-thirds distance from base is assumed to be the reduced exopod; exopod one-quarter length of combined basipod and endopod, basal width half length, narrowing gradually for three-quarters its length then more suddenly to one-third basal width, tip rounded.

Third pereiopod very large, two-thirds length of body, biramous, the rami lamellar, directed posteriorly and separated but fused with base which is one-fifth length of subequal rami; exopod a flattened subsemiovate lamella, basal width two-thirds length, narrowing slightly distally, distal margin rounded, hiding the egg strings in lateral view; the endopod is folded almost into a right angle in cross section, the inner portion lying flat against egg strings, the outer portion turned ventrally, involving one-quarter width of endopod distally, less proximally, the ventrally turned portion lying almost parallel to exopod, endopod if flattened would be subrectangular, width one-quarter length, posterior angles rounded.

page 16

Fourth pereiopod biramous, total length half total length of third pereiopod, rami fused with basipod which is one-quarter length of exopod and narrows towards its base so that its lateral margins form entire curves with outer margin of exopod and inner margin of endopod; exopod one-quarter as wide at the base as long, narrowing and rounded distally, outer margin a convex curve, inner margin sublinear, with a very small spine on a raised boss on outer margin near junction with basipod; endopod three-quarters exopod length, width at midpoint half length, narrowed slightly proximally, more narrowed distally, rounded distally, outer margin an entire curve, inner margin sublinear.

Fifth pereiopod borne near midpoint of genital segment lateral margin, almost as long as genital segment, width one-quarter length, rounded distally, bent into a right angle, directed laterally, then posteriorly, with a small seta on a well developed projection near distal margin.

Discussion

The material on hand agrees well with Thomson's description and figures (1889, p.366-7, pl. 27, figs. 2a-j); this could be expected in the case of the Otago Museum material since it had been identified as L. percis by Thomson himself.

Wilson (1936, p.340) claimed to have found this species on Promicrops itaira at the Dry Tortugas. The only description he gives is that the first antennae "prove to be six-segmented, with no setae except two minute ones at the tip of the end segment". Since in A. percis the antenna is seven segmented with setae on every segment it seems that Wilson's record is of yet another species of Aethon.

A. percis resembles A. quadratus Krøyer in its general form and in its possession of forked, unsegmented, second pereiopods, and in the development of the third pereiopods, but it can be separated from A. quadratus in that the latter has the posterior lateral lobe of the cephalothorax extending out well beyond the anterior (which may even be missing; Krøyer does not make this clear) while in A. percis the posterior lobe is only slightly longer than the anterior. Further, A. quadratus has a well developed neck region, almost entirely missing in A. percis.

Aethon garricki n.sp.

Material

From gills of Cheilodactylus macropterus: One female collected by the author from Somes Island, Wellington Harbour, 28 April, 1961.

Description

Female (figs. 51-63).

Overall length 3.82 mm.

Cephalothorax subovate, width two-thirds length (1.22 mm × 0.86 mm), anterior and posterior margins sublinear, lateral margins entire convex curves, anterior margin half cephalothorax width, posterior margin three-quarters cephalothorax width; antennae carried laterally on an anterior area one-quarter cephalothorax length, half cephalothorax width posteriorly, slightly narrower anteriorly, distinguished by very faint grooves; cephalothorax without lateral expansions.

Second and third thoracic segments fused, distinguishable by a dorsal and lateral transverse groove, combined length two-thirds width, width of second segment four-fifths width of third (combined length 0.81 mm, width of second thoracic segment 1.04 mm, width of third thoracic segment 1.24 mm); two poorly developed dorsal plates which are rounded laterally, cover much of the dorsum of each segment; page 17

Aethon garricki n.sp. female: fig. 51: dorsal view; fig. 52: lateral view; fig. 53: ventral view; fig. 54: first antenna; fig. 55: second antenna; fig. 56: mouth tube and mandibular palp; fig. 57: maxilla; fig. 58: maxilliped; fig. 59: first pereiopod; fig. 60; second pereiopod; fig. 61: fourth pereiopod; fig. 62: genital segment, abdomen and caudal laminae; fig. 63: caudal lamina.

page 18 lateral margins of these segments are extended in wing like projections which increase width of segments by up to one-third the extensions rounded anteriorly, extended posterolaterally for a distance equal to half length of combined second and third thoracic segments, this extension narrowing rapidly and ending in a blunt point, this extension well separated from the plate of the fourth thoracic segment.

Fourth thoracic segment, including plate, subovate, anterior margin sublinear, width two-thirds length (1.96 mm × 1.36 mm), lateral margins forming an entire curve with posterior margin except that posterior margin has a median convex invagination, one-ninth segment length, one-fifth segment width. The segment is entirely covered by the plate in dorsal view and the single specimen was not dissected so that the segment itself was not seen.

Genital segment subrectangular, slightly swollen posteriorly, length three-quarters width (0.33 mm × 0.46 mm).

Abdomen subcircular, length four-fifths width (0.32 mm × 0.39 mm), caudal laminae borne posteroventrally.

Caudal laminae width two-fifths length (0.12 mm × 0.05 mm), subtriangular, lateral margins irregular, with a lateral projection one-quarter distance from base, one-fifth as long as lamina, a little wider than long, and tipped with a sharp spine; lamina with a further sharp spine at the distal apex, and a further spine on medial margin near the apex.

Egg strings long, complexly coiled and hidden indorsal view by the plate of the fourth thoracic segment, in ventral view by the third pereiopods.

First antenna of seven subrectangular segments, ratio of lengths from the basal segment outwards being approximately 3:3:2:3:1:1:1; first segment width two-thirds length, second segment width four-sevenths length, with three setae on outer margin, third segment as wide as long, with two small setae on outer margin, fourth segment width half length, with one long and one short seta on outer margin, fifth segment as wide as long, with one small seta on outer margin, sixth segment as wide as long, with one small and one large seta on outer distal angle, seventh segment rounded distally, width three-quarters length, with one small seta on outer margin and six setae on distal margin.

Second antenna of two segments, subchelate; first segment, basal width two-thirds length, narrowing to three-quarters this width distally, curved, with a stout spine on inner margin near base; second segment basal width half length, narrowing steadily to a sharp point distally, strongly curved, with a stout spine near inner margin one-third of distance from base.

Mouth tube small (0.2 mm in length), sharply pointed distally.

Mandibular palp, with two rami on a flattened subrectangular base; outer ramus, width one-third length, rounded distally, with two small and one large setae distally; inner ramus half length of outer, width two-thirds length, rounded distally, with one seta distally.

Maxilla of two segments, segments subequal in length; first segment, basal width two-fifths length, narrowing slightly distally, distal margin rounded; second segment basal width one-seventh length, narrowing gradually distally except that distal seventh narrows suddenly; a small process, half length of narrowed distal region is situated on inner margin at base of this region.

Maxilliped of two segments, subchelate; first segment, basal width half length, narrowing slightly distally, distal margin rounded, with a small spine one-third of distance from base; second segment basal width two-fifths length, narrowing gradually to a distal point, sharply curved over distal half.

page 19

First pereiopod biramous, each ramus of one segment; basipod swollen, subsemicircular, length two-thirds width, with one small spine medial to endopod and another on a raised boss lateral to exopod; exopod subovate, subequal in length to basipod, width half length, with five flattened spines on distal margin; endopod subtriangular, subequal in length to exopod, basal width half length, distal apex bearing a spine.

Second pereiopod biramous, the rami fused to the basipod, length including rami more than twice length of first pereiopod, as long as basal width, narrowing steadily distally, to end in a sharp point, the terminal section presumed to include the endopod, distal portion curving sharply medially and posteriorly away from the body, inner margin with a well developed subtriangular expansion one-third distance from base, and a process on outer margin two-thirds distance from base is assumed to be the reduced exopod; exopod one-quarter length of combined basipod and endopod, basal width half length, narrowing gradually for three-quarters its length then more suddenly to one-third basal width, tip rounded.

Third pereiopod very large, half length of body, biramous, the rami lamellar, directed posteriorly and separate but fused with base which is one-fifth length of subequal rami; exopod a flattened subsemiovate lamella, basal width two-thirds length, narrowing slightly distally, distal margin rounded, hiding the egg strings in lateral view; endopod with a sharply curved section near outer margin, the inner portion lying flat against egg strings, the outer portion turned ventrally, to form a shallow ridge which lies parallel to the exopod, endopod if flattened would be subrectangular, width one-quarter length, posterior angles rounded.

Fourth pereiopod biramous, total length half total length of third pereiopod, rami fused with basipod which is one-quarter length of exopod and narrows towards its base so that its lateral margins form entire curves withouter margin of exopod and inner margin of endopod; exopod one-quarter as wide at the base as long, narrowing and rounded distally, outer margin a convex curve, inner margin sublinear, with a very small spine on a raised boss on outer margin near junction with basipod: endopod three-quarters exopod length, width at midpoint half length, narrowed slightly proximally, more narrowed distally, rounded distally, outer margin an entire curve, inner margin sublinear.

Fifth pereiopod borne near midpoint of genital segment lateral margin, almost as long as genital segment, width two-fifths length, rounded distally, bent so as to be directed posterolaterally, then posteriorly, with a small seta on a well developed projection near distal margin.

Discussion

A. garricki can be separated from A. quadratus Krøyer 1836 and A. percis (Thomson, 1889) by the lateral margins of the cephalothorax which are entire curves, without the well developed lateral lobes found in the other species.

Aethon morelandi n.sp.

Material

On the gills of Latridopsis ciliaris (moki)—three females from Ngaraunga, Wellington, collected by W. Heaphy on 7 August, 1951 (Dominion Museum collection).

Description

Female (figs. 64-77).

Overall length 4.45 mm - 4.71 mm.

Cephalothorax, length nine-tenths width (1.25 mm - 1.33 mm × 1.36 mm - 1.46 mm) anterior and posterior margins sublinear, antennae carried laterally on an anterior page 20 area which is two-fifths cephalothorax length, one-quarter cephalothorax width, and which is marked off laterally by shallow grooves, and extends anteriorly a little beyond remainder of anterior margin of cephalothorax, anterior margin of anterior area very slightly curved; anterior quarter and posterior three-quarters of lateral margin expanded as two rounded lateral lobes, the anterior one directed laterally, posterior one directed anterolaterally.

Second and third thoracic segments fused, the junction between them marked by a transverse groove running dorsally and laterally, second segment nine-tenths width of third, overall length six-tenths width of third (second segment width 1.12 mm - 1.41 mm, third segment width 1.31 mm - 1.61 mm. overall length 0.77 mm - 0.85 mm); the combined segments are extended laterally as wing-like projections, which may increase width of segment by up to two-fifths, lateral margins sublinear, anterior angles rounded, posterior angles extended posterolaterally for a distance equal to two-fifths segment length, free margins slightly serrate.

Fourth thoracic segment including plate, width nine-tenths length (2.32 mm - 2.61 mm × 2.17 mm - 2.46 mm), subovate, with slightly developed blunt posterolateral angles, posterior margin divided into two entire curves by a median concave invagination which is one-tenth segment length, one-eighth segment width, margin of plate slightly serrated. Fourth segment completely covered by plate, a little narrower than plate, but less than one-third its length (0.6 mm).

Genital segment subovate, length three-fifths width (0.39 mm × 0.65 mm).

Abdomen subcircular, as long as wide (0.56 mm × 0.55 mm), caudal laminae carried posteroventrally.

Caudal laminae very small, length twice width (0.18 mm × 0.09 mm), subtriangular, lateral margins irregular, with a lateral projection one-quarter distance from base, one-fifth as long as lamina, a little wider than long, and tipped with a sharp spine; lamina with a further sharp spine at the distal apex, and a further spine on medial margin near the apex.

Egg strings long, complexly coiled and hidden in dorsal view by the plate of the fourth thoracic segment, in ventral view by the third pereiopods.

First antenna of seven subrectangular segments, ratio of lengths from the basal segment outwards being approximately 3:3:2:3:1:1:1; first segment width two-thirds length, second segment width four-sevenths length, with three setae on outer margin, third segment as wide as long, with three setae on outer margin, fourth segment width half length, with five setae on outer margin, fifth segment as wide as long, sixth segment as wide as long, with two long setae on outer distal angle and one small seta on distal margin, seventh segment rounded distally, width three-quarters length, with one small seta on outer margin and six setae distally.

Second antenna of two segments, subchelate; first segment, basal width half length, narrowing to three-quarters this width distally, curved, with a stout spine on inner margin near base; second segment, basal width half length, narrowing steadily to a sharp point distally, strongly curved, with a stout spine near inner margin one-quarter of distance from base.

Month tube small (0.25 mm in length), sharply pointed distally.

Mandibular palp, with two rami on a flattened subrectangular base; outer ramus width two-fifths length, rounded distally, with one long and one short seta distally; inner ramus half length of outer, width two-thirds length, rounded distally.

Maxilla of two segments, segments subequal in length; first segment basal width two-fifths length, narrowing slightly distally, distal margin rounded; second segment page 21

Aethon morelandi n. sp. female: fig. 64: dorsal view; fig. 65; lateral view; fig. 66: ventral view; fig. 67: first antenna; fig. 68: second antenna; fig. 69: mouth tube and mandibular palp; fig. 70: maxilla; fig. 71: tip of maxilla; fig. 72: maxilliped; fig. 73: first pereiopod (dorsal view); fig. 74: second pereiopod; fig. 75: fourth pereiopod; fig. 76: genital segment, abdomen and caudal laminae; fig. 77: caudal lamina.

page 22 basal width one-fifth length, narrowing gradually distally except that distal one-fifth narrows suddenly and bears two longitudinal rows of small spines reaching almost to the slightly blunted tip, with two flattened spines lying transversely at distal end of rows; a small process, one-third length of narrowed distal region, width half length, is situated near inner margin one-third distance from tip, and bears two setae distally, the larger seta subequal in length to process, the other a little smaller.

Maxilliped of two segments, subchelate; first segment, basal width two-thirds length, narrowing slightly distally, distal margin rounded; second segment basal width half length, narrowing gradually to a distal point, sharply curved over distal two-thirds.

First pereiopod biramous, each ramus of one segment; basipod swollen, subsemicircular, length two-thirds width, with one small spine medial to endopod and another on a raised boss lateral to exopod; exopod subovate, subequal in length to basipod, width two-thirds length, with five flattened spines on distal margin; endopod subtriangular, subequal in length to exopod, basal width half length, without spine, but spine may have been lost.

Second pereiopod biramous, the rami fused to the basipod, length including rami more than twice length of first pereiopod, as long as basal width, narrowing steadily distally, to end in a sharp point, the terminal section presumed to include the endopod, distal portion curving sharply medially and posteriorly away from the body, inner margin with a well developed subtriangular expansion one-third distance from base which is tipped with a flattened disc-shaped process, and a process on outer margin two-thirds distance from base is assumed to be the reduced exopod; exopod one-quarter length of combined basipod and endopod, basal width half length, narrowing gradually for three-quarters its length then more suddenly to one-third basal width, tip rounded.

Third pereiopod very large, two-thirds length of body, biramous, the rami lamellar, directed posteriorly and separate but fused with base which is one-fifth length of subequal rami; exopod a flattened subsemiovate lamella, basal width two-thirds length, narrowing slightly distally, distal margin rounded, hiding the egg strings in lateral view; the endopod is folded almost into a right angle in cross section, the inner portion lying flat against egg strings, the outer portion turned ventrally, involving one-quarter width of endopod distally, less proximally, the ventrally turned portion lying almost parallel to exopod, endopod if flattened would be subrectangular, width one-third length, posterior angles rounded.

Fourth pereiopod biramous, total length half total length of third pereiopod, rami fused with basipod which is one-quarter length of exopod and narrows towards its base so that its lateral margins form entire curves with outer margin of exopod and inner margin of endopod; exopod one-quarter as wide at the base as long, narrowing and rounded distally, outer margin a convex curve, inner margin sublinear, with a very small spine on a raised boss on outer margin near junction with basipod; endopod three-quarters exopod length, width at midpoint half length, narrowed slightly proximally, more narrowed distally, rounded distally, outer margin an entire curve, inner margin sublinear.

Fifth pereiopod borne near midpoint of genital segment lateral margin, almost as long as genital segment, width half length, rounded distally, bent into a right angle, directed laterally, then posteriorly, with a small seta on a raised boss near distal margin.

Discussion

A. morelandi can be separated from A. garricki since its cephalothorax possesses lateral lobes which are lacking in the latter. A. morelandi lacks the well developed page 23neck round in A. quadratus and also has the posterior lateral lobe of the cephalothorax less well developed.

A. morelandi most closely resembles A. percis but can be distinguished from it by the anterior lobe of the cephalothorax which projects laterally, not posterolaterally as in A. percis, and by the posterior margin of the fourth thoracic segment plate which is not as strongly curved as in A. percis and has more clearly defined posterolateral angles.